Pilot Spray Research Articles

Dissolution enhancement of a poorly water-soluble antimalarial drug by means of a modified multi-fluid nozzle pilot spray drier

A spray drier with a modified multi-fluid nozzle was used to prepare microparticles of a poorly water-soluble antimalarial drug, artemisinin (ART), with the aim of improving its dissolution in water. ART was co-spray dried with a hydrophilic polymer, polyethylene glycol (PEG). The differential scanning calorimetry and X-ray diffraction studies showed that the crystallinity of ART decreased after spray drying. Compared to the physical mixture of ART and PEG, the amorphous phase of ART in the spray dried ART–PEG composites increased, which depended on the weight ratio of drug to polymer. The phase-solubility studies revealed that the aqueous solubility of ART was improved by the presence of PEG. The dissolution of ART from the spray dried ART–PEG composites was more rapid than that from their respective physical mixture and the original ART powder. For example, the dissolution of ART from the spray dried ART–PEG composite (1:6) was 6.5 times higher than that from the original ART powder in the first 30min. In the mathematical modeling, the Weibull and Korsemeyer–Peppas models were found to best fit to the in vitro dissolution data and then the drug release mechanism was considered as the Fickian diffusion.

Multi-zone modelling of partially premixed low-temperature combustion in pilot-ignited natural-gas engines

Detailed results from a multi-zone phenomenological simulation of partially premixed advanced-injection low-pilot-ignited natural-gas low-temperature combustion are presented with a focus on early injection timings (the beginning of (pilot) injection (BOI)) and very small diesel quantities (2–3 per cent of total fuel energy). Combining several aspects of diesel and spark ignition engine combustion models, the closed-cycle simulation accounted for diesel autoignition, diesel spray combustion, and natural-gas combustion by premixed turbulent flame propagation. The cylinder contents were divided into an unburned zone, several pilot fuel zones (or ‘packets’) that modelled diesel evaporation and ignition, a flame zone for natural-gas combustion, and a burned zone. The simulation predicted the onset of ignition, cylinder pressures, and heat release rate profiles satisfactorily over a wide range of BOIs (20–60° before top dead centre (before TDC)) but especially well at early BOIs. Strong coupling was observed between pilot spray combustion in the packets and premixed turbulent combustion in the flame zone and, therefore, the number of ignition centres (packets) profoundly affected flame combustion. The highest local peak temperatures (greater than 2000 K) were observed in the packets, while the flame zone was much cooler (about 1650 K), indicating that pilot diesel spray combustion is probably the dominant source of engine-out emissions of nitrogen oxide (NO x). Further, the 60° before TDC BOI yielded the lowest average peak packet temperatures (about 1720 K) compared with the 20° before TDC BOI (about 2480 K) and 40° before TDC BOI (about 2700 K). These trends support experimental NO x trends, which showed the lowest NO x emissions for the 60°, 20°, and 40° before TDC BOIs in that order. Parametric studies showed that increasing the intake charge temperature, pilot quantity, and natural-gas equivalence ratio all led to higher peak heat release rates and hotter packets but the pilot quantity and intake temperature affected the potential for NO x formation to a greater extent.

Influence of two-stage injection and exhaust gas recirculation on the emissions reduction in an ethanol-blended diesel-fueled four-cylinder diesel engine

The purpose of this study is to investigate the effects of two-stage injection and exhaust gas recirculation (EGR) on the spray behavior and exhaust emission characteristics in diesel–ethanol fuel blends fueled four-cylinder diesel engine. The spray behavior is analyzed from the spray development process, spray tip penetration, and spray cone angle, which are obtained from the spray images. The combustion and exhaust emission characteristics are measured from the four-cylinder diesel engine with a common-rail injection system. The experimental results revealed that the increase of the pilot injection amount causes the fast development of the injected pilot spray, and the penetration difference among the main sprays is less than that among the pilot sprays. An increase in the ethanol blending ratio causes an increase in the ignition delay in the pilot combustion, but the main combustion is little influenced by the ethanol blending. The increase in the pilot injection amount shows the reduction effects of NO x emissions when the pilot injection timing is advanced beyond BTDC 20°. The concentration of soot emissions shows a decreasing pattern according to the advance of the pilot injection and the decrease in the pilot injection amount. The CO emissions increase with the advance of the pilot injection timing, the increase in the pilot injection amount, and the ethanol blending ratio. In addition, the increase in the ethanol blending ratio and the advance of the pilot injection timing induce an increase in the HC emissions. The increase in the pilot injection amount induces a slight increase in the HC emissions.

Prediction of Powder Stickiness along Spray Drying Process in Relation to Agglomeration

The spray drying process consists of a fast convective drying of liquid droplets by hot air. Initially, the water activity (aw) of a drop is close to 1. During drying, the drop surface aw decreases while viscosity increases until reaching a sticky rubbery state before further drying. This can be observed for products such as carbohydrates, leading to particles sticking on walls (product losses) or to adhesion between particles leading to agglomeration. In this study, particle stickiness was investigated in a cocurrent pilot spray dryer by measuring drying air properties (temperature and relative humidity) at different positions. This allowed describing the evolution of temperature and mean water content of the drying drops. Two model products (maltodextrin DE12 and DE21) were spray dried varying process parameters liquid flow rate (1.8, 3.6, and 5.4 kg/h), air temperature (144°, 174°, and 200°C), airflow rate (80–110 kg/h), and rotary atomizer speed (22,500–30,000 rpm). The two products exhibit different drying behaviors in relation to their affinity towards water (sorption isotherms) and glass transition temperature evolution with aw (stickiness). Depending on drying conditions and product, the drop stickiness was observed very rapidly, close to the atomizer, or later, along the chamber. This approach can be used to identify conditions and positions corresponding to sticky particles.

Spray Drying of Suspensions for Pharma and Bio Products: Drying Kinetics and Morphology

An experimental investigation of the spray drying behavior of droplets containing excipients and carrier materials used in the pharmaceutical and biotechnological industries has been conducted. Specifically, rice starch suspensions with different amounts of TiO2, maltodextrin, dextrin, NaCl and Na2SO4 are dried. The drying rate is measured, and the morphology formation is mapped to obtain a more fundamental understanding of the drying process, which is very useful when designing product formulations. In the pilot spray dryer, droplet generation is based on the JetCutter technology and the droplets are dried under well-defined temperature and flow conditions. The droplets are sampled during drying to determine the drying rate, and the dried particles are collected for morphology analysis. The results show that reducing the water activity in a suspension of insolubles by adding various amounts of inorganic salts or carbohydrates causes an increase in the droplet temperature during spray drying resulting in a rather constant the drying rate. Further, the results show that small alterations in the droplet composition may significantly change the final particle morphology. The observed morphologies are discussed in detail.

Powder agglomeration during the spray-drying process: measurements of air properties

Instant food powders are usually produced by spray drying of formulated liquid and powder agglomeration, either into the drying chamber or in an external fluid bed. During spray drying, according to the liquid composition, the viscosity of the initial liquid drops increases more or less rapidly, until the drop surface reaches a rubbery state considered as sticky, before further drying. This sticky property may be used to produce agglomerates inside the chamber by adding dry solid particles, as fines. The present study deals with a methodology to identify regions where the drying drops are sticky in relation to drying conditions (inlet air temperature 144-159-174 ◦ C, liquid flow rate 15 to 75 mL·min −1 ), using a co-current pilot spray dryer with rotary atomizer. Assuming that drying air properties' (temperature and humidity) evolution is representative of drop drying (drying rate, amount of evaporated water), we realized a map of temperatures and relative humidity for drying air inside the drying chamber. Trials were performed with water (feasibility) and a maltodextrin aqueous solution (40% w/w, DE12) as a model product with sticky properties during drying. The results showed that drying behavior was different for water and aqueous maltodextrin solution. For both, in the tested conditions, the percentage of evaporated water was found to vary from 57 to 89% in the top part of the chamber, close to the atomizer. That represents a possible region where dry fines could be introduced for agglomeration. spray drying / agglomeration / stickiness

A Novel Way to Measure the Concentration of a Spray in a Spray Dryer

A new experimental technique to capture milk concentrate droplets from inside a 150-kg powder/h pilot spray dryer is presented. The technique uses liquid nitrogen to capture the droplets in the dryer and to preserve their moisture content. The droplets are kept frozen until the moisture content can be measured. This technique can be applied to sample the sprays from any semi-commercial-scale spray dryer or similar apparatus.

Sensitivity Analysis of NOx Formation Kinetics in Pilot-Ignited Natural Gas Engines

A sensitivity analysis of NOx formation in pilot-ignited natural gas dual fuel engines is performed based on a phenomenological combustion model. The NOx formation mechanism employed in this study incorporates a super-extended Zel’dovich mechanism (up to 43 reactions). The sensitivity analysis compares the contribution of each major reaction to NOx formation, and identifies the rate-controlling NOx formation reactions in different high-temperature regions—the burning pilot spray, the premixed flame associated with the gaseous fuel-air mixture, and the burned combustion products. The formation rates for reactions involving NOx are also investigated to reveal the primary NOx formation paths. Results show two main NOx formation paths both in the pilot spray (also called the packets zone) and the burned zone. The rate-limiting reactions for the packets zone are O+N2=NO+N and N2+HO2=NO+HNO. Rate-limiting reactions for the burned zone are N2O+M=N2+O+M and N2+HO2=NO+HNO. Since the aforementioned reactions significantly influence the net NOx prediction, it is important that the corresponding reaction rates be determined accurately. Finally, because the quasi-steady-state assumption is commonly used for certain species in NOx modeling, a transient relative error is estimated to evaluate the validity of the assumption. The relative error in NOx prediction with and without the use of the steady-state assumption is small, of the order of 2%. This work also confirms that sensitivity analysis can provide valuable insight into the possible NOx formation pathways in engines and improve the ability of current prediction tools to obtain more reliable predictions.

Spray Dryers: Modeling and Simulation

ABSTRACT This work presents a simulation study of the spray dryer operation using the whole milk suspension as the emulsion to be dried. Two approaches are used to obtain a general description of this operation. The first approach comprises a population balance model, in which drops and particles make up the discrete phase and are distributed into temporal compartments following their residence time in the dryer. Air is the continuous and well-mixed phase. Mass and energy balances are developed for each phase, taking into account their interactions. Constitutive model equations to describe the drop swelling and drying mechanisms as well as the heat and mass transfer between particles and hot air are also analyzed. The set of algebraic-differential equations obtained in this approach is solved by DASSL numerical code. The second approach involves a three-dimensional model solved by a computational fluid dynamic (CFD) code. The continuous air phase follows the time-averaged Navier-Stokes equations coupled with the RNG turbulence model while particle equations are set up in the Lagrangian model using the stochastic method to predict the particle trajectories. Experiments carried out in a pilot spray dryer generate input data for both model approaches. Results are compared to lead to a better understanding of the spray dryer operation.

Modeling and simulation of milk emulsion drying in spray dryers

This work aims at modeling and simulating the drying of whole milk emulsion in spray dryers. Drops and particles make up the discrete phase and are distributed into temporal compartments following their residence time in the dryer. Air is the continuous and well-mixed phase. Mass and energy balances are developed for each phase, taking into account their interactions. Constitutive equations for describing the drop swelling and drying mechanisms as well as the heat and mass transfer between particles and hot air are proposed and analyzed. A set of algebraic-differential equations is obtained and solved by specific numerical codes. Results from experiments carried out in a pilot spray dryer are used to validate the model developed and the numerical algorithm. Comparing the simulated and experimental data, it is shown that the model predicts well the individual drop-particle history inside the dryer as well as the overall outlet air-particle temperature and humidity.

Coating Uniformity: Influence of Atomizing Air Pressure

The objective of this study was to investigate the influence of atomizing air pressure on the coating uniformity and the quality of the film coat. As parameters describing the coating uniformity, the mass variance of the film coated tablets and the variance of the film thickness within a tablet were used. For the examination of the properties of the film coat, the cumulative frequency of the tablet mass, the spray loss, the relative frequency of the film thickness, the minimum amount of polymer required for an enteric coating, and the swelling number were taken into consideration. For this study a Walther Pilot spray gun WA 50 with a liquid orifice diameter of 0.5 mm and a flat jet air cap was used. The experiments were carried out in a Bohle BLC 5 drum coater using four different atomizing air pressures between 0.5 and 2.0 bar. All other parameters were kept constant during the coating process. It could be shown that atomizing air pressure is an important factor influencing the quality and uniformity of a film coat. An increase in the atomizing air pressure will produce smooth tablets with a small mass variance. Due to a greater spray loss, the required minimum amount of polymer for an enteric coating is higher at an atomizing air pressure of 2.0 bar.

Influence of spray drying conditions on functionality of dried whole egg

AbstractInstead of traditional liquid eggs, more and more dried whole egg products are being used in the manufacture of fine bakery goods, since dried semi‐finished products have some advantages regarding storage, handling and microbiological safety. However, the spray drying process leads to changes in sensitive egg components, eg proteins, and affects the functional properties of whole egg after reconstitution. Knowledge of the influence of drying conditions on the resulting functionality is necessary to enable the production of dried egg with tailor‐made properties for applications in different food products. Some of these relationships were determined using a pilot spray dryer for drying experiments and an appropriate statistical evaluation of the results. It could be demonstrated that higher temperatures during spray drying lead to a considerable decrease in the foaming properties of whole egg powder but increase the capability of emulsion stabilisation. Additionally, a simplified example demonstrates the use of these relationships for the selection of optimal drying conditions of whole egg with respect to its application in a cake with higher fat content.© 2002 Society of Chemical Industry

SPRAY DRYING DYNAMIC MODELING WITH A MECHANISTIC MODEL

ABSTRACT In this work we suggest the dynamic modeling of a spray dryer considered as a series of well-stirred dryers. That is, a series of dryers in which the output variables are equal to the state variables. The state equations were obtained from the heat and water mass balances in product and air. Additionally, heat and water mass balances in interface jointly with water equilibrium relation between product and air were considered. A pilot spray dryer was modeled assuming one, two, five and 20 well stirred steps. Low-fat milk with 10–20% of solids was dried at different inlet air temperatures (120–160°C), air flow rate of 0.19 kg dry air s−1 and different feed rates (1.4 − 4.2 × 10−4 kg dry solids s−1). Stationary result showed that the model predicts the experimental air outlet temperature, at different inlet conditions with a maximum deviation of 6°C. The dynamic simulation reproduce the experimental one with moderate accuracy. Experimental dynamic showed that the pilot plant spray dryer has a well-stirred process behavior. The model represents a method for estimate outlet product moisture as function of the outlet air temperature. This has application for automatic control because there is not an easy way to measure on-line measure the outlet product moisture content.

Robustness of a proportional-integral with feedforward action control in a plant pilot spray dryer

Quadratic performance index variations with respect to the dynamic parameters of a PI control with feedforward action in a plant pilot spray dryer were obtained by simulation. Dynamics of plant pilot spray dryer was assumed as first order, using outlet product humidity as response variable and air temperature, moisture and flow, and product moisture and flow as input variables. Initial time constants and gains were obtained experimentally in a plant pilot spray drying with a drying chamber of 1.3 m 3. Control action was simulated by taking air flow as action variable. Thus, air temperature may be altered, and therefore a complementary air temperature control was implemented. The results show that PI control tuning by Routh criteria is robust with respect to variation in time constants and gains. The main performance indexes remain in the same magnitude order when the dynamic characteristics were changed to 80%.

Visualization of Spray Dynamics in a Pilot Spray Dryer by Laser-Initiated Fluorescence

Spray dynamics were examined by means of laser-initiated fluorescence (LIF). These experiments reveal extensive and intermittent dynamic effects. The extent of spray intermittency is a strong function of the water flow rate. The area fraction occupied by the spray correlates (R2 = 0.81) with the ratio of water momentum input to air momentum input. The area fraction is also strongly affected by secondary air feeds or withdrawals. The measured spray field was compared with the predictions of the PSI-Cell model, a numerical, steady-state model that combines interactive heat, mass, and momentum transfer effects and a k − e representation of turbulence. The model predicts the basic shape of the spray and approximate internal conditions. Turbulent droplet dispersion and vortical structures resulting from the shear at the edge of the jet are likely causes of spray intermittency.

An experimental study of flue gas desulfurization in a pilot spray dryer

AbstractMore than 45 experimental tests have been conducted on a 10,000 Nm3/h spray‐drying desulfurization pilot plant. The effects of SO2 and fly ash concentration, Ca/S ratio, approach to saturation temperature, unit load changes, and the utilization of seawater as make‐up water on both spray dryer behavior and treated flue gas properties were analyzed. This experimental study allows us to reach some conclusions about how to achieve optimum operating conditions and to assess the impact of spray drying on a downstream ESP.

An Experimental Study on the Performance of a Multifuel Engine : (Part 2. Effect of Pilot Injection of Fuel)

The idea that the ignition lag of the main spray can be reduced by a preceding injection of pilot spray has been investigated several times. This means was found effective to realize multifuel operation of a conventional diesel engine. In order to realize pilot injection, many ideas have been conceived, but in this study two independent injection pumps and one common nozzle were employed. First, an investigation was made to determine whether injection characteristics of the proposed injection system were suitable for practical engine operation or not, and desirable results could be obtained. Secondly, we attempted at the operation of a pre-chamber diesel engine on low cetane fuel, and excellent results could be obtained with pilot injection if automotive gasoline was used. And the reduction in the ignition lag of the main fuel was caused mainly by the pre-reaction of the pilot fuel.